1. Field of the Invention
The invention relates to a machine for the production of a multi-layer fiber stock web, specifically a paper or cardboard web.
2. Description of the Related Art
Couching of various layers during paper production has hitherto been accomplished by a couching roll, which is typically designed as a perforated cylinder. The forming belt, together with the second layer, or fiber stock web on it, are guided around this roll so that the roll is submerged into the continuous ribbon which is formed by a forming belt or wire supporting the first fiber stock web. Pressure resulting from the tension of the forming belt or wire supporting the first fiber stock web or layer is exerted upon both layers or fiber stock webs.
Prior to couching of a fiber stock web, the second fiber stock web is held to the couch roll only by the binding forces between the second fiber stock web and the second forming belt or wire.
In machinery and methods of the type known in the art there is the risk at high speeds, that the second fiber stock web will separate from the second forming belt or wire prior to couching, due to centrifugal force. This may result in a tangential throwing off of the fiber stock web, resulting in a related waste factor.
What is needed in the art is a device for the production of a multi-layer fiber stock web which would ensure that the second layer does not separate from the forming belt, or wire in the critical area prior to couching.
The present invention provides a device and method in which the second fiber stock layer, in the area prior to the point at which it comes into contact with the first fiber stock layer, is drawn with suction force to the second forming belt, or wire. The second fiber stock layer is admitted specifically in the direction of the couching element. This second fiber stock layer is admitted in an area toward the second forming belt or wire, where this forming belt or wire is in contact with the couching element, or in the area it is diverted by the couch element, or in the area in which it wraps around the couch element.
This simple and reliable method ensures that the second layer does not separate from the second forming belt or wire in the critical area prior to couching. The appropriate handling additionally ensures that the web""s dry content is increased.
In another embodiment of the invention, the couch element is formed by a support element having a surface area which is at least partially open faced and this support element is operated with an interior pressure which is lower than the ambient pressure. The couch element may, for example be a suction roll, a perforated cylinder or a shoe.
Advantageously, the second layer can be subjected to a suction force, which is produced by at least one suction zone in the couch element.
Following the couch element, the forming belt or wire delivering the first layer accepts the second layer. The second forming belt or wire is appropriately separated from the first forming belt or wire in the discharge area of the couch element.
In order to ensure delivery of the web, even at high speeds, it is advantageous if the second layer, in the area in which the two forming belts or wires exit from the couch element, can be pushed away from the couch element by means of fluid over pressure. This second layer separation from a forming belt may specifically be accomplished with air and/or steam. If steam is utilized as the pressure fluid, then a viscosity change of the two couched layers occurs enhancing the subsequent dewatering of the web. For example, a steam blow box or similar device may be provided.
In yet another embodiment of the invention, the fluid excess pressure is produced by at least one pressure zone in the couch element.
The method according to the invention is characterized by the second layer being directed specifically through suction force toward the second forming belt or wire, prior to the point at which it comes into contact with the first layer.
The invention may also be utilized specifically at machinery speeds of higher than 1000 m/min. The fiber stock webs that are to be couched may be created by optional methods, using optional formers (i.e. hybrid formers, gap formers, long wires, crescent formers, etc.), for example, the following Voith Sulzer formers may be utilized: DuoFormer Base, DuoFormer Top, DuoFormer D K, DuoFormer D, TopFormer F, etc. Any combination of various sheet forming methods are also possible.